2970dx-150 Class A

[dxhound]

Hello, I just purchased a 2970dx-150 and was thinking of Biasing the driver, finals and final PA for 50 Watts class A. Just wondering if anyone has done this before.

 

[dxhound]

Alot of views but no comments. Ill give it a try and report back on performance. Ill do a before and after on the specan to see what the IMD and Out of Band Distortion are.

 

[Shockwave]

If that radio uses the inexpensive MOSFET finals in the amp stage, I'd steer clear of the class A mod for sure. They are already under stress and often have stability issues. Adding this much forward bias can only complicate the situation even with the reduced power.

 

[dxhound]

If that radio uses the inexpensive MOSFET finals in the amp stage, I'd steer clear of the class A mod for sure. They are already under stress and often have stability issues. Adding this much forward bias can only complicate the situation even with the reduced power.

Hi Shockwave,
NO, luckily this is the older Bipolar Version with 2166 Driver and 1969 final. The PA uses dual 2290s in push pull config.

I am shooting for 50 watts as long as I dont exceed the current rating on the transistors and the radio does not get too hot. If I can not reach 50 watts I will use as much forward bias as possible. I am shooting for 50 watts because I want to use this radio into a modified TSdx1600. I am adding 4 independent voltage regulation circuits to the amplifier to achieve a stable and temp. compensated bias voltage. I will then use the SSB delay switch as a switchable bias from AB to A. I will no longer need the delay because I am adding a Keyline.

I know this will have little diff from AB to A on the rx end, But I am just looking to tinker

 

[Shockwave]

In that case, you have a much better foundation to work with.

 

[DCinDC]

The beauty of an RF amp is that it can be biased far lower than AB.

Go learn about RF amps and you'll see that your goal is a waste of time.

This ain't HiFi.

 

[Shockwave]

The beauty of an RF amp is that it can be biased far lower than AB.

Go learn about RF amps and you'll see that your goal is a waste of time.

This ain't HiFi.

You might want to look up the Yaesu FT-1000MP Mark V. The class A option for an RF amplifier is about reducing inter modulation distortion.